Excellent Piezoelectric Response Research Articles

Simulation study of ZnO nanorod geometry for the development of high-performance tactile sensors and energy harvesting devices

ZnO exhibits an excellent piezoelectric response and can transduce mechanical energy into electrical signals by applying pressure. In particular, vertically aligned ZnO nanorods were thought to be of great importance because of their higher value of piezoelectric coefficient along the z-direction. In this study, various geometries of ZnO nanorods are explored and their effect on the strength of piezoelectric output potential is simulated using COMSOL Multiphysics software. The simulation results show that out of many geometries and inclinations of ZnO nanorods, the highest piezoelectric output is demonstrated by the inclined ZnO nanorods due to the application of higher torque force or shear stress in similar applied force. The high torque force or shear stress at 60° orientation and optimized contributions from all the piezoelectric coefficients resulted in a high piezoelectric output potential close to 215 mV which is much higher than the vertically aligned ZnO nanorod which is approximately 25 mV.

Progress in manufacturing and processing of Al-Sc alloy targets

The development of the fifth-generation mobile communication technology (5G) puts forward higher requirements for radio frequency (RF) filters. Due to its higher frequency and larger bandwidth, bulk acoustic wave (BAW) filter will become the mainstream RF filter solution. Scandium doped aluminium nitride (AlScN) piezoelectric film has attracted much attention due to its excellent piezoelectric response coefficients and electromechanical coupling coefficients. The doped Sc concentration will directly affect the piezoelectric coefficient and electromechanical coupling coefficient of the film. The most common technique for producing AlScN thin films is magnetron sputtering of targets made of Al-Sc alloy. However, with the increase of Sc content, the solid-liquid solidification interval, the number of intermetallic compounds, and the brittleness of the material will all increase significantly. Additionally, it will result in component macro-segregation, uneven phase distribution, and poor processing deformability. Therefore, it is extremely difficult to manufacture and process Al-Sc alloy targets. The mainstream processes for preparing Al-Sc alloy targets are divided into direct reaction method and powder metallurgy method. This paper reviews the research progress in manufacturing and processing of Al-Sc alloy targets.

Remarkable Enhancement of Piezoelectric Performance by Heavy Halogen Substitution in Hybrid Perovskite Ferroelectrics

Piezoelectric materials that enable electromechanical conversion have great application value in actuators, transducers, sensors, and energy harvesters. Large piezoelectric (d33) and piezoelectric voltage (g33) coefficients are highly desired and critical to their practical applications. However, obtaining a material with simultaneously large d33 and g33 has long been a huge challenge. Here, we reported a hybrid perovskite ferroelectric [Me3NCH2Cl]CdBrCl2 to mitigate and roughly address this issue by heavy halogen substitution. The introduction of a large-size halide element softens the metal-halide bonds and reduces the polarization switching barrier, resulting in excellent piezoelectric response with a large d33 (∼440 pC/N), which realizes a significant optimization compared with that of previously reported [Me3NCH2Cl]CdCl3 (You et al. Science2017, 357, 306-309). More strikingly, [Me3NCH2Cl]CdBrCl2 simultaneously shows a giant g33 of 6215 × 10-3 V m/N, far exceeding those of polymers and conventional piezoelectric ceramics. Combined with simple solution preparation, easy processing of thin films, and a high Curie temperature of 373 K, these attributes make [Me3NCH2Cl]CdBrCl2 promising for high-performance piezoelectric sensors in flexible, wearable, and biomechanical devices.

Piezoelectric-enhanced photocatalytic performance of porous carbon nitride nanosheets.

Through the utilisation of mechanical energy, piezocatalysis and piezophotocatalysis have emerged as promising strategies to tackle the current energy and environmental issues. In this work, porous graphitic carbon nitride (g-C3N4) nanosheets were synthesised via a novel self-templating process followed by ultrasonic exfoliation to produce materials with a thickness of 1.5-2nm and a high specific surface area of 59.48m2/g. Piezo-response force microscopy (PFM) indicated that the as-prepared porous g-C3N4 nanosheets show excellent piezoelectric response. Moreover, the porous g-C3N4 nanosheets exhibit remarkable piezophotocatalytic degradation of Rhodamine B (RhB), showing an optimal first-order rate constant (k=0.301min-1) under visible light and ultrasonic co-excitation, which was 2.3 times the value under visible light irradiation alone and 9.7 times the value under only ultrasonic excitation. A piezoelectric field generated by ultrasonic excitation drove photogenerated electrons and holes in opposite directions to migrate towards the surface of the nanosheets, resulting in the generation of more reactive radicals and thereby accelerating RhB degradation. By highlighting the potential of porous g-C3N4 nanosheets as a piezo-semiconductor for environmental remediation applications, this study paves the way for developing a new method for converting solar and mechanical energy via a piezo-mediation photocatalytic reaction.

Accelerated discovery of high-performance piezocatalyst in BaTiO3-based ceramics via machine learning

The study of piezocatalysis has become an important topic in piezoelectric research, especially for addressing environmental issues. However, the reliance on nanofabrication seriously hinders investigating materials with complex compositional design for higher performance and large-scale application. In this work, we use a machine learning strategy to efficiently sample the vast compositional space for ceramic powders with excellent piezoelectric response that we expect to impact piezocatalytic performance. The ceramics, synthesized by solid state reaction methods, belong to the multi-component system (Ba1−x−yCaxSry)(Ti1−u−v−wZruSnvHfw)O3 with target property d33, the piezoelectric coefficient. The highest d33 tends to occur within the phase boundary region with coexisting rhombohedral, orthorhombic and tetragonal phases, especially on the rhombohedral phase side. We select (Ba0.95Ca0.05)(Ti0.9Sn0.1)O3 as it combines a relatively large d33 with the fewest number of elements. Its sintered ceramic exhibits a high d33 of 605 ± 14 pC/N, consistent with the machine learning prediction 633 ± 70 pC/N. The mechanically-ground ceramic powders have an excellent piezocatalytic activity with a degradation rate of (2.16 ± 0.28) × 10−2 min−1 for RhB dye solution, comparable to the performance of previously reported nanoparticles. Our work provides further insight into the nature of piezoelectricity in BaTiO3 based ceramics, and affords an effective strategy for searching for superior piezocatalysts suitable for large-scale applications.

Lead titanate nanowires/polyamide-imide piezoelectric nanocomposites for high-temperature energy harvesting

With an increasing demand for self-powered microelectronics to be used in scientific tasks and exploration missions in extreme environments, the implementation of piezoelectric energy harvesting at high temperature is an important research focus for renewable energy sources. Piezoelectric composites made from piezoelectric ceramic fillers and polymer matrices combine high electromechanical coupling with flexibility, resulting in a versatile candidate for energy harvesting. In this research, a nanocomposite formed by lead titanate nanowires (PbTiO3 NWs) and a polyamide-imide (PAI) matrix is developed and shown to have an excellent piezoelectric response at high temperatures. By in situ measurements of the piezoelectric g31 and d31 coefficients of the nanocomposite films with different PbTiO3 NW weight fractions in the temperature range 25–250 °C, the dependence of temperature and filler concentration on the piezoelectric properties are fully characterized. In addition, the effect of NW alignment on piezoelectric properties through direct ink writing is also studied. Finally, a bending-mode energy harvester made from this nanocomposite is demonstrated to generate a maximum power density of 33 μW·m−2 at resonance and a power density of 20 μW·m−2 under low-frequency random excitation at 200 °C, while keeping a long operating life of at least 100 h. In conclusion, this work provides a new solution for high-temperature energy harvesting from low-frequency random vibrations using PbTiO3/PAI nanocomposites.

Negative Piezoelectric Coefficient in Ferromagnetic 1H-LaBr2 Monolayer.

The discovery of two-dimensional (2D) magnetic materials that have excellent piezoelectric response is promising for nanoscale multifunctional piezoelectric or spintronic devices. Piezoelectricity requires a noncentrosymmetric structure with an electronic band gap, whereas magnetism demands broken time-reversal symmetry. Most of the well-known 2D piezoelectrics, e.g., 1H-MoS2 monolayer, are not magnetic. Being intrinsically magnetic, semiconducting 1H-LaBr2 and 1H-VS2 monolayers can combine magnetism and piezoelectricity. We compare piezoelectric properties of 1H-MoS2, 1H-VS2, and 1H-LaBr2 using density functional theory. The ferromagnetic 1H-LaBr2 and 1H-VS2 monolayers display larger piezoelectric strain coefficients, namely, d11 = −4.527 pm/V for 1H-LaBr2 and d11 = 4.104 pm/V for 1H-VS2, compared to 1H-MoS2 (d11 = 3.706 pm/V). 1H-MoS2 has a larger piezoelectric stress coefficient (e11 = 370.675 pC/m) than 1H-LaBr2 (e11 = −94.175 pC/m) and 1H-VS2 (e11 = 298.100 pC/m). The large d11 for 1H-LaBr2 originates from the low elastic constants, C11 = 30.338 N/m and C12 = 9.534 N/m. The sign of the piezoelectric coefficients for 1H-LaBr2 is negative, and this arises from the negative ionic contribution of e11, which dominates in 1H-LaBr2, whereas the electronic part of e11 dominates in 1H-MoS2 and 1H-VS2. We explain the origin of this large ionic contribution of e11 for 1H-LaBr2 through Born effective charges (Z11) and the sensitivity of the atomic positions to the strain (du/dη). We observe a sign reversal in the Z11 values of Mo and S compared to the nominal oxidation states, which makes both the electronic and ionic parts of e11 positive and results in the high value of e11. We also show that a change in magnetic order can enhance (reduce) the piezoresponse of 1H-LaBr2 (1H-VS2).

Homogenous Sn-doped K(Ta,Nb)O3 single crystals and its high piezoelectric response

Perovskite K(Ta,Nb)O3 (KTN) single crystal has drawn great interests for its outstanding electro-optic performance and excellent piezoelectric response. However, growth of compositionally uniform KTN single crystals has always been a great challenge for the great segregation difference between Nb and Ta. In this work, we propose a thermal field optimization strategy to resolve this challenge. Homogenous Sn doped KTN (Sn:KTN) single crystal with significantly reduced composition gradient (0.003 mol/mm, 1/4–1/8 of other KTN system), minimal TC variation (13 °C) and excellent piezoelectric and dielectric response (d33 = 373 pC/N and ε33T = 5206) has been successfully achieved. We found that the functional properties of Sn:KTN were greatly affected by the near-room temperature tetragonal-cubic phase transition. From the intrinsic aspect, longitudinal lattice deformation becomes much easier, resulting in maximum piezoelectric (d33∗), dielectric (ε33T∗), elastic (s33E∗)and electromechanical coupling (k33∗) coefficients along polar direction [001]C. From the extrinsic aspect, both domain wall density and domain wall mobility are greatly improved for the reduced lattice distortion, which also contribute a lot to the functional properties. This work provides a simple and practical route for designing and growing high quality crystals, and more importantly, reveals the fundamental mechanism of the phase transitions/boundaries on the functional properties.

Highly sensitive, reliable and flexible pressure sensor based on piezoelectric PVDF hybrid film using MXene nanosheet reinforcement

The rapid advances in intelligence terminal devices have raised expectations for highly sensitive, reliable and flexible pressure sensor. Herein, we present a highly sensitive flexible pressure sensor based on piezoelectric MXene/poly(vinylidene fluoride) (PVDF) hybrid film. Making use of MXene nanosheet reinforcement, one can efficiently promote the piezoelectric output and consequently sensitivity of PVDF. For instance, upon a small loading of 0.4 wt%, the piezoelectric coefficient d33 of MXene/PVDF hybrid film reaches the peak of 43 pC/N. Meanwhile, the incorporation of MXene nanosheet is advantageous to strengthen the mechanical performance of PVDF. With the excellent piezoelectric response and mechanical property, the MXene/PVDF hybrid film sensor demonstrates to perform superior voltage sensitivity up to 0.0480 V/N, which is double that of PVDF based sensor. Meanwhile, the novel hybrid film sensor also exhibits fast recovery time of 3.1 ms and stable operation capability under cyclic force, confirming their applicability as reliable pressure sensor.

Robust Polarization Stability in a Self‐Assembled Ultrathin Organic Ferroelectric Nano Lamellae

AbstractSpontaneous polarization is a characteristic feature of a ferroelectric material that can be switched by the application of an external electric field. However, in a practical scenario, the switched polarization should be stable for the realization of functional devices. In this study, an ultrathin (≈40 nm) poly(vinylidene fluoride‐trifluoroethylene (PVDF‐TrFE) film self‐assembled on a monolayer (≈1 nm) graphene oxide (GO) film is exploited. Oxygen‐functional groups and defective structure of GO can act as domain pinning sites to provide strong ferroelectric domain stability along with a specific crystal orientation to PVDF‐TrFE through hydrogen bonds and columbic interactions. Scanning probe microscopy based switching experiments reveal excellent piezoelectric response (d33 = −145 pm V−1) along with high polarization retention (over 1500 h with no volatilization) in these ultrathin films, paving new pathways toward high performance miniaturized organic ferroelectric devices.

A large piezoelectric voltage coefficient in aluminate-sodalite-type improper ferroelectric oxides

An excellent piezoelectric response has been demonstrated in the aluminate-sodalite-type oxides (Ca1−xSrx)8[AlO2]12{MoO4}2, around the MPB-like vertical phase boundary, shedding light on the development of eco-friendly piezoceramics with excellent functionalities.

Confinement Aided Simultanous Water Cleaning and Energy Harvesting Using Atomically Thin Wurtzite (Wurtzene)

AbstractSyntheses of few‐layered piezocatalysts from nonlayered materials have gained a huge attention of attention in recent years due to their potential applicability in efficient removal of toxic elements from water. Here, a simple scalable bottom up approach consisting of wet‐chemical synthesis method is used to produce the atomically thin (2D)‐wurtzite ZnO: “wurtzene.” The presence of a large number of well‐distributed surface defects in the synthesized wurtzene promotes the separation of charge carriers in it via the excellent piezo‐photocatalytic activity and thereby the efficiency of degradation of a test dye (namely methylene blue) is enhanced by ≈5 times. By taking an innovative approach, a piezoelectric driven power cell is also fabricated by using the wurtzene and the highest open circuit voltage is found out to be ≈40 V at 1.0 kPa of applied periodic pressure. The experimental observations are explained with density functional theory calculation. The confinement effect due to reduced dimension plays a crucial role in the wurtzene's excellent piezoelectric response. It is envisioned that the present findings will provided a clear insight into the synthesis of wurtzene with surface defects for highly efficient sunlight driven photocatalytic activity as well as piezoelectric energy harvesting.

Sensing Ability of Ferroelectric Oxide Nanowires Grown in Templates of Nanopores.

Nanowires of ferroelectric potassium niobate were grown by filling nanoporous templates of both side opened anodic aluminum oxide (AAO) through radiofrequency vacuum sputtering for multisensor fabrication. The precise geometrical ordering of the AAO matrix led to well defined single axis oriented wire-shaped material inside the pores. The sensing abilities of the samples were studied and analyzed in terms of piezoelectric and pyroelectric response and the results were compared for different length of the nanopores (nanotubes)—1.3 µm, 6.3 µm and 10 µm. Based on scanning electronic microscopy, elemental and microstructural analyses, as well as electrical measurements at bending and heating, the overall sensing performance of the devices was estimated. It was found that the produced membrane type elements, consisting potassium niobate grown in AAO template exhibited excellent piezoelectric response due to the increased specific area as compared to non-structured films, and could be further enhanced with the nanowires length. The piezoelectric voltage increased linearly with 16 mV per micrometer of nanowire’s length. At the same time the pyroelectric voltage was found to be less sensitive to the nanowires length, changing its value at 400 nV/µm. This paper provides a simple and low-cost approach for nanostructuring ferroelectric oxides with multisensing application, and serves as a base for further optimization of template based nanostructured devices.

Highly Tunable Molecularly Doped Flexible Poly(dimethylsiloxane) Foam Piezoelectric Energy Harvesters

Despite considerable research interest in developing piezoelectric materials, little work has focused on the fundamental design of these materials from the ground up. Herein, we present a general, versatile method for producing tunable, flexible piezoelectric energy harvesters (PEHs) with excellent piezoelectric response. Using a poly(dimethylsiloxane) (PDMS) foam derived from a sugar template, we separate the electrical and mechanical properties of the PEH, thereby allowing us to optimize them separately. The electrical properties were tuned by varying the poling field, the polar dopant, and the dopant concentration. The mechanical properties were tuned by varying foam preparation and thus the compressive modulus. Through the careful tuning of these properties, we are able to achieve a maximum piezoelectric response of 153 pC/N, which is considerably higher than that of most other reported flexible PEHs. Combined with our previous work, we demonstrate that doping polymer foams with polar dopants is a highly general strategy and has the potential to lead to materials with considerably higher piezoelectric responses.

Boosting piezoelectric response of KNN‐based ceramics with strong visible‐light absorption

AbstractA series of (1 − x)(K0.48Na0.52)NbO3‐x(Bi0.5Na0.5)(Zr0.55Ni0.45)O3‐δ (KNN‐BNZN) ceramics are designed to achieve excellent piezoelectric response along with narrow bandgap. The ceramics with x = 0.04 exhibit unprecedented piezoelectric coefficient d33 ~ 318±10pC N−1 in comparison with all reported narrow bandgap ceramics. A rhombohedral‐orthorhombic‐tetragonal (R‐O‐T) phase boundary is observed, indicating the formation of defect dipoles (Ni2+‐) at morphotropic phase boundary region is desirable for piezo‐/ferroelectric properties. In addition, a narrow bandgap ~2.5 eV along with gap states (~0.9 eV and ~1.6 eV) is obtained from the ceramics when x > 0.02, which can be persuasively explained by the schematic plot of bandgap splitting mechanism proposed in this work, where Ni 3d energy state plays a role as a scaffold in the process of electron transition. More importantly, largely enhanced photovoltaic performance of the ceramics is achieved under AM 1.5 irradiation. The NIR photoresponse property (maximum current density of ~100 nA cm−2) indicates such KNN‐based ceramics with sub bandgap ~ 0.9 eV may even have potential to be applied in NIR light‐activated devices. Our findings might pave way for the further development of piezoelectric/photoresponsive multifunctional devices.

Low electric field-induced strain and large improvement in energy density of (Lu0.5Nb0.5)4+ complex-ions doped BNT–BT ceramics

The (Bi0.5Na0.5)0.94Ba0.06Ti(1 − x)(Lu0.5Nb0.5)xO3 (BNBT–xLN, x = 0, 0.02, 0.03, 0.04, 0.05, 0.07) ceramics were designed to investigate their dielectric, ferroelectric, energy storage and electrostriction properties. All ceramics illustrated single pseudo-cubic perovskite structure and densely stacked microstructure. The LN doping disturbed the long-range ordered ferroelectric phase, which was confirmed by the depressed P–I–E loops and S–E curves. The excellent piezoelectric response was realized in the coexistence region of the ferroelectric polar and weak-polar phases. A significant enhancement of electric field-induced strains (Smax = 0.42%) with a large average normalized strain coefficient (d33* = Smax/Emax) of 602.41 pm/V, electrostriction coefficient (Q33 = 0.0334 m4/C2) was achieved at x = 0.02. And a high energy storage density of 0.72 J/cm3 was obtained at x = 0.03. As a result, the systematic investigations on the BNBT–xLN ceramics can benefit the developments of low electric field piezoelectric and energy storage devices.

Enhanced Piezoelectric Properties and Temperature Stability of 0.5BZT-0.5BCT Ceramic Induced by Using Three-Step Synthesizing Method

(1-x)BaZr0.2Ti0.8O3-xBa0.7Ca0.3TiO3 (BZT-xBCT) system is a lead-free piezoelectric material with excellent piezoelectric response. But the temperature instability has seriously restricted the application of this system. In this work, the influence of precursor and synthesizing method on the piezoelectric temperature stability has been studied. And the results show that the piezoelectric temperature stability could be substantially improved by using suitable precursor and synthesizing method. The BZT-0.5BCT ceramic synthesized by using three-step synthesizing method has a huge piezoelectric constant (d33 = 668 pC/N) and meanwhile has a good temperature stability. The SEM and XRD analysis show that the excellent piezoelectric properties are related to ceramic grain size and phase structure. Moreover, our result provides a simple and efficient method to improve the piezoelectric properties of the BZT-0.5BCT system and could accelerate application process of the ceramics.

Durable, efficient, and flexible piezoelectric nanogenerator from electrospun PANi/HNT/PVDF blend nanocomposite

Currently, there is considerable research focus on portable, lightweight, shock‐resistant, and inexpensive wearable devices that are ideally powered by harvesting abundant mechanical or vibration energy, making battery or related wiring superfluous. In this study, piezoelectric nanogenerator was electrospun from PANi (polyaniline)/HNT (halloysite nanotube)/PVDF (poly[vinylidene fluoride]) blend nanocomposite. Polymorphism, crystallinity and morphology of the nanogenerator were explored in detail. HNT and PANi acted as a nucleating agent and conductive filler, respectively in PVDF; their synergism helps improve the piezoelectric performance of PVDF. The piezoelectric performance of the nanogenerator patch was studied under various external mechanical stresses, such as pressure, tapping, and impact. A maximum voltage output of approximately 7.2 V was generated by the nanogenerator under impact. The nanogenerator patch attached to human arm exhibited not only excellent piezoelectric response during arm movements, but, also proved to be flexible, highly sensitive and durable. This nanogenerator could possibly be used in wearable piezoelectric energy conversion application for self‐powered devices. POLYM. COMPOS., 40:1663–1675, 2019. © 2018 Society of Plastics Engineers

Thermal annealing and single–domain preparation in tetragonal Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 crystal for electro–optic and non–linear optical applications

The relaxor–PbTiO3 single crystal has attracted extensive attention in ultrasound transducers, sensors, actuators, and optoelectronics devices due to its excellent piezoelectric response and electro–optic properties. Preparation of a single–domain crystal as a critical process for application in electro–optic and non–linear optical devices suffers from serious and inevitable cracking. Therefore, a pre-poling thermal annealing process was suggested to release residual stress from crystal growth and the ferroelectric–paraelectric phase transition, which significantly reduced the chance of cracking. The effect of thermal annealing on dielectric properties, strain behavior, and domain structure were investigated. As a result, a significant increase of the dielectric constant near room temperature was obtained after annealing, which is close to the dielectric constant of the a-oriented domain. The annealed single crystal showed a lower and sharper strain peak at the coercive electric field compared with the unannealed sample, and the 90° domain walls completely vanished, which was verified by optical microscopy. The crack–free single–domain crystal showed excellent optical quality, with high transmittance of approximately 70% in the visible and near–infrared regions, which indicates that this crystal is a promising candidate for applications in electro–optic and non–linear optical devices.

A modified barbell-shaped PNN-PZT-PIN piezoelectric ceramic energy harvester

The quaternary system of relaxor-ferroelectric based Pb(Ni1/3Nb2/3)O3-Pb(ZrxTi1−x)O3-Pb(In0.5Nb0.5)O3 (PNN-PZT-PIN) piezoelectric ceramic at the morphotropic phase boundary was investigated via the solid reaction method. The optimized ceramic with excellent electric properties of εr = 8084, d33 = 977 pC/N, kp = 0.61, and Ec = 3.0 kV/cm was fabricated into d33-mode discs with separated surface electrodes, which were arranged in a series connection and, then as a piezo-stack, assembled into a barbell-shaped energy harvester that could bear a strong mechanical vibration. It is found that under a vibration mass-induced bending moment, the energy harvester produces an open circuit voltage of 26.4 Vp-p at the acceleration of 2.5 g at a load of 1.56 MΩ, which is two times higher in comparison to one without surface electrode separation. Its power output is 30 μW at the acceleration of 1 g and 104 μW at 2.5 g, which are even six times higher than that of a previously reported barbell-shaped energy harvester at room-temperature with the same acceleration. The enhanced power output can be attributed to (i) the excellent piezoelectric response of PNN-PZT-PIN ceramic and (ii) harvesting positive and negative charges from the separated surface electrodes other than a full surface electrode on piezoelectric discs under bending moment. Furthermore, the practical test was performed within a car engine, which shows that the PNN-PZT-PIN piezoelectric ceramic is a promising candidate for vibration energy harvesting.